The invention relates to a water-cooled cylinder head for a multicylinder internal-combustion engine. The preferred embodiment relates to a water-cooled cylinder head for a multicylinder internal-combustion engine having two inlet and outlet valves per cylinder, comprising a cylinder head cooling space with inflow and outflow openings for the coolant which is integrated in a cylinder head housing and extends above a part-spherical cap forming a combustion chamber volume. Water cooling spaces are formed at least in areas around a receiving opening for a spark plug arranged centrally in the cylinder head housing and around two outlet valves. The water cooling spaces are mutually connected by way of a common water cooling jacket annulus section.
Particularly in high-performance engines, temperature peaks of up to 300° C. occur, despite water-cooled cylinder heads and because of the high specific performance, particularly in areas between the outlet valves or between the outlet valves and the spark plugs. These temperature peaks result in temperature stress in the material and, in connection with external loads, in permanent deformations in the valve seat ring areas of the outlet valves.
It is therefore an object of the invention to overcome the above-mentioned disadvantages and to improve the cooling in the highly stressed areas of the cylinder head housing.
This object is achieved according to certain preferred embodiments of the invention by providing a water-cooled cylinder head for a multicylinder internal-combustion engine having two inlet and outlet valves per cylinder. The cylinder head includes a cylinder head cooling space with inflow and outflow openings for the coolant which is integrated in a cylinder head housing and extends above a part-spherical cap forming a combustion chamber volume. Water cooling spaces are formed at least in areas around a receiving opening for a spark plug arranged centrally in the cylinder head housing and around two outlet valves. The water cooling spaces are mutually connected by way of a common water cooling jacket annulus at section. At least the common water cooling jacket annulus section has a volume which remains an essentially constant distance from the combustion chamber volume, so that, at least in this area, the wall thickness of the part-spherical combustion chamber cap extends in a uniform manner and so as to close to the combustion chamber volume.
Since the joint water cooling jacket annulus section between the two outlet valves and the receiving opening for the spark plug has a volume remaining an essentially constant distance from and extending close to the combustion chamber volume, the temperature peaks in this area can be effectively reduced. Instead of high-temperature cylinder head alloys, such as AlCu5Ni1,5CoSbZr, it is thus also possible to use less expensive standard alloys, such as AlSi6Cu4 or AlSi7MG. On the other hand, by lowering the temperature, the knocking tendency of the engine is reduced, so that, because of the ignition angle improvements, consumption advantages and a corresponding power increase can be achieved.
Additional advantageous features of preferred embodiments of the invention are described herein and in the claims.
According to certain preferred embodiments of the invention, for a fast and effective heat dissipation in the area of the spark plug dome, it is suggested to reduce the diameter of the receiving opening for the spark plug at the level of the joint water cooling jacket annulus section. This can be implemented by constructing the thread of the spark plug in this area with an outside diameter which is reduced with respect to the spark plug housing.
Tests have shown that optimal cooling of the highly stressed points is ensured with a simultaneously sufficient dimensional stability, particularly of the part-spherical combustion chamber cap, when the wall thickness of the spherical combustion chamber cap is reduced, at least in the area of the joint annulus section, to between 5 and 11 mm, according to certain preferred embodiments of the invention.
According to certain preferred embodiments of the invention, an additional cooling duct in the form of an injector bore ensures that the joint annulus section is directly supplied with cooling water.
According to certain preferred embodiments of the invention, another improvement or optimization of the cooling of the cylinder head housing is achieved when the water cooling jacket in the area of the spherical combustion chamber cap and of the inlet and outlet ducts monitored by the valves has an essentially uniform wall thickness between 3 and 7 mm. As a result of the constant water cooling jacket thickness, higher flow rates of the cooling water can be achieved and the heat transmission can thereby be improved.
According to certain preferred embodiments of the invention, adequate cooling is achieved by a main cooling flow which extends between the two outlet valves in the direction of the receiving opening for the spark plug, while two secondary cooling flows are formed on the outside on the two outlet valves.
According to certain preferred embodiments of the invention, by means of a targeted throttling of the two secondary cooling flows by corresponding contractions in the corresponding cooling ducts, it is ensured that the main cooling quantity is guided directly into the spark plug area.
The drawings illustrate an embodiment of the invention which will be described in detail in the following.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.